Transmission control system



April 16, 1957 w. l.. sHl-:PPARD TRANSMISSION CONTROL SYSTEM Filed April13, 1953 April 16, 1 957 w. l.. SHEPPARD 2,788,678

TRANSMISSION CONTROL SYSTEM Filed April 13. 19'53 3 Sheets-Sheet 2 April16, 1957 w. L.. SHEPPARD 2,788,678

TRANSMISSION CONTROL SYSTEM iled April 13, 1953 3 Sheets-Sheet 3 zal(,742 E:

Gob. Tres Vres.

TRANSMISSION CONTROL SYSTEM William L. Sheppard, Romulus, Mich.,assignor to Chrysler Corporation, Highland Park, Mich., a corporation ofDelaware Application April 13, 1953, Serial No. 348,485

26 Claims. (Cl. 74-645) This invention relates to hydraulic controlsystems for motor vehicle power transmission units and the like, andparticularly to an improved type of shift control valve unit for suchsystems.

It is a primary object of this invention to provide a two-piece,differential pressure operated, shift control valve unit of simplifieddesign that is designed such that fast, positive, valve shifting may bereadily accomplished upon variation in the relationship between theopposed pressure fluids applied to the valve elements of the valve unit.

It is a further object of this invention to provide a simplied form oftwo-piece, differential pressure operated, shift control valve whereinat least one of the pressure iluids applied to the valve elements isarranged in such a manner as to accomplish snap action shifts of thevalving in each of its directions of control movement.

It is still another object of this invention to provide a two-piece,dilerential pressure operated, shift control valve unit with anassociated `operator controlled kickdown valve arranged in such a mannerthat a rst relatively low pressure fluid can be applied to the valveelements of the valve unit to initiate a kickdown or driver `controlleddownshift, and thereafter, when the valve elements approach apredetermined point of movement towards their downshifted position, asecond relatively high pressure fluid is applied to the valve elementsto accomplish a snap action downshift or kickdown of the valve elementsto their desired positions.

Other objects and advantages of this invention will become readilyapparent from a reading of the following description and a considerationof the related drawings wherein:

Fig. 1 is a diagrammatic plan view of a motor vehicle having a powertransmission unit embodying this invention;

Fig. 2 is a schematic diagram of the power transmission unit utilized inFig. 1;

Fig. 3 is a diagrammatic view of a hydraulically operated control systemfor the power transmission unit shown in Fig. 2, which control systememploys shift valves embodying this invention;

Fig. 4 is an enlarged sectional elevational view of one of thedifferential pressure operated, speed ratio shift valve units of thedisclosed transmission control system which valve unit embodies thisinvention; the valves thereof being shown in their downshiftedpositions;

Fig. 5 is an enlarged sectional elevational view similar to Fig. 4 butshowing the valves of the valve unit upshifting and at the snap overposition;

Fig. 6 is an enlarged sectional elevational view similar to Fig. 4 butshowing the valves of the valve unit snapped over to their upshiftedpositions;

Fig. 7 is an enlarged sectional elevational view similar to Fig. 4showing the valves of the valve unit at the beginning of a kickdown fromtheir upshifted positions;

Fig. 8 is an enlarged sectional elevational view similar to Fig. 4showing the valves of the valve unit at the snap CAB 2,788,678 PatentedApr. i6, i957 over position during a kickdown from their upshiftedpositions; and

Fig. 9 is an enlarged fragmentary sectional elevational view similar toFig. 4 but showing a modified form of valve with a throttle responsivedownshift.

Fig. l diagrammatically discloses a conventional motor vehicle powerplant and drive train comprising an internal combustion engine Edrivingly connected through a hydrokinetic type of torque converter unitA to a change speed gear box B. The output from gear box B drives apropeller or drive shaft P that transmits drive to the rear wheels W ofthe vehicle through the rear driving axles X. Engine E includes theusual carburetor F with a carburetor accelerator pedal G.

Fig. 2 of the drawings diagrammatically discloses the power transmissionunitwhich comprises the hydrokinetic torque converter unit A and theplanetary type change speed gear box B arranged in series drivetransmitting relationship. This transmission unit is specificallyclaimed in the copending application of Bert W. Cartwright, Serial No.308,123, tiled September 5, 1952. Converter unit A is adapted todrivingly connect a prime mover such as the motor vehicle engine E tothe input shaft of transmission gear box B. The reference numeral 8 inFig. 2 represents the rear end portion of the engine crankshaft of themotor vehicle power unit E. The crankshaft 8 is drivingly connected tothe casing portion 9 of the converter A. Within converter casing portion9 are mounted the various converter components, namely, the impellcrmember 11i, the turbine or runner member 15, and the guide wheel orreaction member 17.

The vaned impeller wheel 14 is iixedly connected to the converter casing9 and is accordingly adapted to be rotatably driven by the engine drivencrankshaft 8. The vaned turbine wheel 15 is drivingly connected to theconverter driven shaft 16. The converter driven shaft member 16 isadapted to transmit drive from the torque converter unit A to the gearbox B arranged rearwardly of and in series with the torque converterunit A.

The vaned guide wheel 17 of the converter is rotatably supported wit-hinthe converter casing 9 by means of a oneway brake device 21. The one-waybrake device 21 is mounted on the forward end of an axially extendingsleeve 32 that is fixed to and projects from the rearwardly positioned,relatively stationary, gear box casing wall 2d. The one-way brake 21 isdesigned and arranged such that it will permit only forward rotarymovement (clockwise when looking from the converter A towards gear box Bof Fig. 2) to be transmitted to guide Wheel 17 by the forward orclockwise rotation of the impeller 14. The brake 2l locks against thesleeve 32 to prevent rotation of the guide wheel 17 in a reverse orcounterclockwise direction.

The torque converter unit A (see Fig. 2) includes a gear type oil pump25 having a driven gear that is directly connected to the axiallyextending, sleeve-like ange portion 9b of the rotatable converter casing9. rl'he pump 25 draws oil from a sump 26 (see Fig. 3) through theconduit 27 and circulates it through the converter unit A, portions ofthe transmission lubricating system, and the various hydraulicallyoperated control mechanisms associated With this transmission unit. Thecirculation of oil through the converter A, by the pump 25, provides ameans for maintaining the converter A full of oil whenever the enginecrankshaft 8 is rotating. A second oil pump 84 driven by thetransmission Output shaft 8l is also included in this power transmissionunit to provide a source of pressure uid when the engine E is notoperating. Pump 84 is connected to oil supply sump 26 (see Fig. 3) byconduit 28 and discharges oil to the same elements as does the enginedriven pump 25.

[The gear box `B is specifically described in the said copendingapplication of Bert W. Cartwright, Serial No.

CII

operating clutch elements carried by the encircling drumshaped member 47of clutch C. Drum-shaped member 47 is drivingly connected to the sungear 49 of the change speed gear box B and thus constitutes the drivenmember of clutch C. Engagement of clutch C is effected by the admissionof pressure fluid to a cylinder bore (not shown) containing theaforementioned clutch elements.

The planetary gearing that is disposed between the clutch C and `theoutput shaft 81 comprises a iirst set of compounded gearing 52 toprovide for the several forward drive ratios and a second set of gearing72 to provide for reverse drive. Forward drive gearing 52 includes thesun gear 53 which is yan integral part of the intermediate `drive shaft16. Sun gear 53 meshingly engages with the short pinion gear members S4of the compounded or double pinion gears 54, 57 that are rotatablymounted on the carrier element 55. Carrier 55 is provi-:led with a sungear portion 73 that forms part of the reverse drive planetary gear set72. Carrier element 55 journals the short pinion gears 54 and it alsojournals the long pinion gears 57. The relatively long pinion gears 57are meshingly engaged with the relatively -short pinion gears 54 andwith the clutch drum mounted sun gear element 49. The long pinion gears57 also have portions thereof surrounded by .and meshingly engaged withthe annulus gear 5S.

Annulus gear 58 is part of a drive transmitting member 59 that isdrivingly connected to the output shaft 81. Drive transmitting member 59includes in addition to the annulus gear portion S8 pinion gear axlesthat journal the pinion gears 74 of the reverse gear set. Pinion gears74 will be further described in lthe following description of reversedrive gear set 72.

rFhe carrier member 55 of gear set 52 has an axially extending brakedrum portion 55a that is adapted to be engaged by a brake band 63. Brakeband 63 is adapted to be `applied to the brake drum portion 55a ofcarrier 5S to anchor carrier 5S against rotation and thereby activateforward drive gear set 52 for the transmission of the Low speed forwarddrive ratio.

It will also be noted that the outer periphery of the drum member 47 ofdirect drive clutch C is encircled by a brake band 65. Application ofbrake band 65 to drum 47 anchors the drum 47 .and the attached sun gear49 against rotation and conditions the forward drive gear set 52 for thetransmission of the Second or Kicked Down speed ratio drive.

From a consideration of Fig. 2, it is thought to be clear that input togear train 52 is from the input or sun gear 53 to the small pinion gears54. Small pinion gears 54 are meshed with and drive the long pinions 57.Long pinions 57 are meshed with and drive annulus gear 58 whenever thereaction brake bands 63 or 65 are applied to elements 55 or 47respectively of the gear train 52 so as to give either Low or Secondspeed forward drive respectively. When clutch C is engaged, then inputgear S3 and reaction gear 49 `of gear train S2 are both drivinglyconnected to the drive shaft 16 so the gear train 52 is then locked upfor the transmission of direct drive.

Arranged rearwardly of the forward drive planetary gearing 52 is asecond set of planetary gearing that is designated generally 'by thenumeral 72. The gear set 72 provides for reverse drive and comprises thesun gear element 73 that is an integral part of the carrier member 55 offorward drive gear set 52. Sun gear 73 meshingly engages with piniongears 74 that are rotatably mounted on the pinion gear carrier 59. Aspreviously mentioned carrier 59 is drivingly connected to the outputshaft 81 and also forms an integral part of the annulus gear 58 of gearset '52 so yit will thus lbe seen that the carrier member 459 providesthe output or drive transmitting member for each of the sets ofplanetary gearing 52, 72. An annulus gear is formed as part of a drummember 76. Annulus gear 75 is arranged in meshing engagement with pinionlgears 74 of the gear set 72. The outer peripheral Iflange of the ydrummember 76 is `encircled by 'a brake zband 77 that is adapted to beapplied to the drum member 76 to anchor same against rotation andcondition gear set 72 for the transmission of a Reverse drive betweenshafts 16 and 81.

Mounted adjacent to and driven by output shaft 81 is the second oil pump84. Oil pump 84 is similar to oil pump 25 and includes adriving gearelement (not shown) that is drivingly connected to the transmissionoutput shaft 81. Oil is withdrawn by pump 84 from the transmission caseoil sump 26 through the conduit 28 (see Fig. 3). Pressurized oil isdistributed '(see IFig. 3) by the pump 84 to the supply for theconverter A and to the hydraulic control system for the transmission aswell as to the pressurized transmission lubrication system.

A hydraulic control system for the hereinbefore described rtr-ansmissionunit, or a similar type of transmission unit, is shown diagrammatica-llyin Fig. 3. The control system includes a vehicle speed responsivegovernor mechanism 87 that would probably be mounted on the output shaft81 of the herein described transmission. This governor 87 is identicalto that described and claimed in William L. Sheppard co-pendingapplication Serial No. 98,493, filed June 11, 1949. yIn addition to thevehicle speed responsive control unit 87, some form of torque regulatingor torque responsive control such 'as a valve operated by the engineaccelerator pedal G is included in this transmission control -system soas to provide both speed and torque responsive control mechanisms :tocontrol operation 'of the transmission.

It -is proposed to have suitable hydraulic controls for thistransmission so as to provide a fully automatic three forward speedsgear box in addition to providing means for selectively locking thetransmission in either of the two forward underdrive ratios and reversedrive.

The control system (see Fig. 3) for this transmission includes themanually operable drive ratio selector lever 111 which is rotatablymounted on the conventional motor vehicle steering column 112. Controllever 111 is connected by suitable Vlinkage 113 to the manually operabledrive ratio selector valve 170. Drive ratio selector valve 170 has tivedrive ratio positions which are represented in the drawings by theletters R, N, D, S and L respectively. These letters correspond to theReverse, Neutral, Drive, Second and Low ratios which ratios areselectively obtainable by manual shift of selector lever 111. The letterV associated with the valve units 120, 170 and with the other valveunits of this control system, denotes a vent or drain port for returningthe control system pressure i'luid to the fluid supply sump 26.

Pressure fluid from either of the supply pumps 25 or 84 is directed intothe main supply conduit 191 which is connected to the manually operabledrive ratio selector valve 170. The pressure of the fluid in supplyconduit 191 is controlled by the pressure regulator valve 185 and thiscontrolled pressure fluid supplied to valve 170 is dcnoted line pressure(normally about p. s. i.) for purposes of description hereafter. Checkvalves 183 and 184 maintained a closed pressure fluid supply system. Onadmission of line pressure iluid to the bore 171 to drive ratio selectorvalve certain of the control mechanisms associated with the controlsystem will be energized and one or the other of the severalaforementioned drive ratios will be established. When the manual valve170 is located in the Neutral position the valve lands 172 and 173 ofplunger or spool type valve element 174 close oti the escape ofpressurized line fluid from valve bore 171 except through conduit 192that leads to the pressure regulator valve 185. Thus line pressure luidcannot pass from supply conduit 191 through valve 170 to activate any ofthe drive ratio control mechanisms. However, it should be noted thatwhen the manually controlled valve 170 is placed in the Neutral positionwith the vehicle engine running, or when the vehicle `is being pushed ortowed so that one or the other of pumps 25 or 84 is operating, linepressure fluid from one or the other of pumps 25, 84 can still bedirected through conduits 192 and 186 to the line pressure regulatorvalve 185 and through valve 185 to the conduit 193 that suppliespressure uid to the converter A. Conduit 1193 may contain a converteruid pressure regulator valve 19S to control the pressure of the fluiddirected into the converter A. Pressure uid passing through converter Ais passed `on to the pressurized transmission `lubrication system andtothe sump 26 by the conduit 194. Conduit 194 may have associatedtherewith a flow restriction -197 and in som-e cases a converter lluidcooling unit 196. The converter pressure regulator valve 19'5 may -beset to maintain a pressure of approximately 55 to 6() p. s. i. in theconverter at all times.

In either of the forward drive ratio positions D or S or L of the driveratio selector valve element 174, line pressure fluid from supplyconduit 191 will always be directed through the bore 171 of valve unit170 and into the connected conduits 119, 119e` that connect the manualdrive ratio selector valve unit 170 with the torque control or torqueregulating throttle valve unit 120. Consequently a form of torqueresponsive control is always available to cooperate with the drivenshaft speed responsive governor 87 Vto conjointly control automaticoperation of this transmission unit in all forward drive ratios. Linepressure passed to conduit 119, whenever the ratio selector valve 170 isset for a start in either Drive, Second or Low ratio, also fills conduit119gl and is passed to and around throttle valve 120 and then to the Lowto Second shift valve 140. It will be noted that the conduit 119e has abranch conduit 159 connected thereto to divert pressurized line7pressure fluid to the bore portion 143 of the shift valve unit 140. Linepressure admitted to valve bore portion 143 is transferred by conduit160 to the apply side 69a of the Low servo 69. Application of linepressure to the apply side of servo 69 applies band 63 and activates thetransmission for the Low or rst speed forward underdrive. Thus theplanetary gear train 52 is initially activated for the Low forwardunderdrive when- Vever valve unit 170 is set for a starting drive ineither Drive or Second or Low, that is, all starts forwardly will bethrough the Low underdrive initially.

The torque responsive throttle valve unit 120 has operably associatedtherewith through linkage 231 a kickdown valve-controlled mechanism 230that is hereinafter described. The torque responsive throttle valve 12dis operated by linkage 116 connected to the throttle control oraccelerator pedal G for the engine unit E that drives this powertransmission unit. The piston type throttle valve element 121 of valveunit 120 is arranged to be reciprocated by oscillation of the linkage116. Throttle valve unit plunger element 121 is arranged to reciprocatein the bore 122 of the valve unit 120 and it is connected to theactuating linkage 116 through a compression spring 124. At closed oridle throttle position of the accelerator pedal G with the manualcontrol valve 170 set for either of the forward drive ratios D, S or L,the arrangement of the plunger valve 121 in the bore 122 of valve 120 issuch as to permit some pressurized fluid `to tlow from the supplyconduit 119e through valve bore 122 of valve 120 and into the conduit125 and its branch conduits 125a and 125b. The pressure of the uidpassing out of valve 120 into conduit 125 may be lower than that of theline pressure supplied to valve 120 by conduit 119e due to the reducingvalve action of valve 121. This reduced or compensated line pressuresupplied to `conduits 125, 12511 and 125b, is denoted throttle pressurehereafter.

Admission of throttle pressure to the branch conduit 12519 permits thisthrottle responsive pressurized iluid to be passed to the conduit 250that includes the check valves 251 and 252 respectively. Conduit 250 isconnected to the bores of valves 140 and 240. Throttle pressure lluidpassed through conduit 250 to the bores 144 and 244 of shift valves 140and 240 respectively can be passed through the conduits 142, 242respectively and be applied to the right ends of the plunger or spooltype valves 145 and 245 of control valves 140 and 240 respectivelywhenever the vehicle is at a stop or traveling at relatively low speeds.Under such conditions the valves M1, 145 and 241, 245 will be positionedtowards the left ends of their respective valve bores and conduit b isthen connected to conduits 142 and 242 and the chambers 146, 246 at theright ends of valves 140, 240. Drive ratio shift control valves and 240are differential pressure operated shift valves that automaticallyelfect the speed ratio shifts between Low and Second and. Second andDirect respectively. The details and the manner of operation of thesedifferential pressure operated control valves are subsequentlydescribed.

Governor pressure fluid from the governor output conduit 98 is passedinto branch conduit 93u which applies the output shaft speed responsivepressurized fluid to the chambers 147, 247 at the left end of valves 140and 24). This governor pressure in the valve bores at the left end ofvalve units 144), 244] tends to urge the plunger or spool-type two-piecevalve elements 141, 14S and 241, 24S, towards the right ends of thevalve units 140, 240. Thus it will be seen that the pressuredifferential between the throttle pressure fluid and the output shaftspeed responsive pressurized lluid, which fluids are applied to oppositeends of valves 141, 145 and 241, 24S, effects reciprocating movement ofthese two-piece connected shift valves within their valve bores. Atrelatively low output shaft speeds with the throttle valve 121 crackedopen, the throttle pressure in conduit 12Sb is greater than the governorpressure in conduit 98a and the valves 141, 145 and 241, 245 areautomatically positioned towards the left ends of their valve bores. Asthe output shaft speed increases a point is reached where the governorpressure from conduit 93u exerts a force on the left end of the valves141, 241 that overcomes the force of the throttle pressure on right endsof the valves 145, 245 and then the two-piece shift valves 141, 145 and241, 245 successively shift towards the right to upshifted positionssuch as that shown in Fig. 6 which correspond to upshifted Direct driveposition of the valves 241, 245. This differential pressure generatedshift of the two-piece shift valves 141, 145 and 241, 245 is utilized toautomatically control operation of the direct drive clutch C and theservos 63 and 69 for the forward drive braking bands e3, 65. lt shouldbe pointed out that the diameters of valves 141, 145 are greater thanthe diameters of valves 241, 245 and thus the same pressurized fluidsadmitted to the valve units 14), 24() will produce different shiftforces and as a result diiferent points are obtainable for the Shiftsfrom Low to Second and Second to Direct. Also connected valves 241, .24Smust work against a spring 243 so this raises the Second to Directupshift point above that of the Low to Second upshift. Upshift of valves141, 145 may occur from about 9 to 1S M. P. H. while upshift of valves241, 245 may occur from about 18-68 M. P. H. lt is thought to be obvious that the points of shift of the shift control valves will varyconsiderably depending on the degree of throttle valve opening ascompared to the output shaft speed at any given time.

After initiating drive in Low the rightward upshift of shift valves 141,145 will connect the bore portion 143 of the valve 140 to vent conduit162 and this will vent the band applying line pressure from Low" servoo9 through the vent valve 161 due to the bore 143 in valve 140connecting the Low servo supply conduit 160 to the the band o or releasechamber 63e of the Second speed control servo 68. This venting ofchamber GSC is due to conduit 168 being connected through the boreportion 259 of valve 240 to the conduit 249 which is also connected tothe bore portion 143 of valve 140 and the vent valve 161. Line pressurethat was directed into band applying chamber 68a of servo 68 during theapplication of the Low band 63 by servo 69 was not previously effectiveto simultaneously apply Second band 65 due to the existence of linepressure in the band off or release chamber 68e of servo 68. However, onventing of the off chamber 68e of Second servo 68 simultaneously withthe venting of the apply chamber 69a of Low servo 69, then Second hand65 is applied as Low band 63 is released. Thus as Low control band 63 isreleased Second control band 65 is applied to effect the upshift toSecond speed. in addition to using line pressure to apply Second band65, throttle pressure is also applied to chamber 68h of servo 68 by wayof conduit 1250 to assist the line pressure in chamber 68a in holdingband 65 applied. Relay valve 166 and shuttle valve 167 also participatein controlling the pressure fluids applied to the several servos but itis not thought that a description of their functions is necessary for anunderstanding of the invention claimed herein.

After the upshift from Low to Second then subsequently the Second toDirect shift valve 240 will effect an automatic upshift from Second toDirect To accomplish this shift line pressure is directed into releasechamber 68e of servo 68 by way of conduit 168 so as to effect release ofSecond band 65. At the same time line pressure is directed by way ofconduit 168a, valve 167, conduit 16M, valve bore 166:1 and throughconduit 16% to the clutch apply chamber 5@ of clutch C. Conduit 169ealso feeds line pressure to conduit 169 for supply to chamber 261 ofvalve 240 to effect elongation of the connected valves 241, 245.Engagement of clutch C effects lock up of planetary 52 so as to providefor the transmission of a forward direct drive from shaft 16 to outputshaft 81. Automatic downshifts from Direct to Second to Low are effectedin the reverse manner to that described for the upshifts.

In addition to the automatic downshifts from Direct to Second to Low, itis possible for the transmission or vehicle operator to overrule theautomatic controls and effect a downshift from Direct to Second atsubstantially any time he desires by merely fully depressing theaccelerator pedal G. Such an accelerator depression will cause linkage116 (see Figs. 3, 7 and 8) to apply linkage 231 to the right end ofkickdown valve 23u and shift valve element 232 to the left. Leftwardshift of valve 232 when the transmission is operating in Direct willbring about an immediate downshift from Direct to Second due to theapplication of a pressurized fluid to the right end of the Second toDirect shift valves 241, 245. When valves 241, 245 are kicked down thenline pressure is supplied to chamber 68a of servo 6% and venting of thebore 50 of clutch C occurs. After the kickdown to Second thetransmission control system will either automatically upshift to Directon release of the depressed accelerator G, or, if the output shaft speedshould be dropping, then possibly the control system would automaticallydownshift to Low for a more favorable speed ratio drive in the startingunderdrive ratio.

In addition to the operator effected, accelerator pedal actuateddownshift, the transmission operator can also downshift from Direct toSecond or Low by manually shifting drive control lever 111 to either theSecond or Low position. This manual shift will lock the transmission inthe particularly selected drive ratio and prevent automatic upshifts ordownshifts therefrom. Locking of the transmission in either the Secondor Low ratio 8 is particularly advantageous for coast braking. It mighbe pointed out that the control system includes valve means 179 in themanual control valve unit 170 to limit the top speed at which the manualdownshift to Low may be'accomplished. If the manual shift to Low isattempted at too high a speed then the transmission will irst downshiftto Second and thereafter, when the speed has dropped sufliciently, willthen downshift to Low and remain locked in the preselected Low ratiountil the control lever 111 is shifted to some other ratio.

Reverse drive is accomplished by setting the drive control lever 111 inthe Reverse position. This causes the control system to pass a boostedline pressure through conduit 181 to the Reverse servo 70 and apply bandto annulus gear 75 so as to condition reverse drive planetary gear set72 for transmission of a reverse drive to output shaft 81. The otherportions of the control system are deactivated at this time so there isno automatic upshiftng or downshifting involved. However, in addition tothe torque effect of the gear set 72 there is also the torquemultiplication of the converter A so a starting reverse drive ratio of19.8 to 1 is possible.

As the invention herein described and claimed does not relate tocontrols generally but the shift valves per se, it is not thought that amore detailed description of the control system is required. Suffice itto say that Vwith the torque converter A having a torque multiplyingstall ratio of 2.5 and with a rear wheel driving axle ratio of 3.1, thenthe table set forth below gives the pertinent information relative tothe driving ratios obtainable with a transmission of this type.

2,5 Torque Converter 3.1 Axle Ratio Drive Ratio Control Gear OverallApplied Ratio Ratio Low (1st) Baud 63 2.69 20. il-S. 35 Kiekdown (2nd)Band G5 1.53 4. 74 Direct (3rd) Clutch C 1. 00 3.10 Reverse Band 77 2.55 19, 8-7. 91

From a consideration of the aforegoing description and the relateddrawings, it is thought to be clear that this transmission provides acompact, rigid, relatively simple gear box that can be combined with ahydrodynamic torque converter device to provide a fully automatic threespeed gear box that will give the required ratios and flexibility inorder to eiciently operate a present day motor vehicle in current trameand on current highways. When forward drive is to be initiated, thecontrols are set in Drive and this will initially apply the Low Band 63to drum 62 and thereby activate gear set 52 for the Low ratio. Byinitially starting in Low or lst speed, the gearing 52 is combined withthe torque multiplication of converter A so as to give a starting driveoverall ratio of as much as 20.9 to l. The control system willthereafter, when speed and torque conditions are satisfactory,automatically release band 63 and apply band 65 to sun gear drum member47 so as to upshift the drive ratio from the Low or lst speed to the 2ndor Kickdown speed ratio drive. Thereafter, when speed and torqueconditions are satisfactory, the control system will again automaticallyupshift the speed ratio drive from the Second ratio to the Direct speedratio by releasing band 65 and engaging direct drive clutch C. Adownshift may be manually accomplished from the Direct drive to both theSecond and the Low ratios. The control system includes means to lock thecontrols in either of the Low or Kickdown ratios so that each of theseratios may be used for coast braking or the like.

The shift control valve units and 241) involvethe invention hereinclaimed. As these valve units 140 and avssve 240 are substantiallyidentical, only the valve unit 240, for controlling the Second to Directupshifts and downshifts, will be described. Figs 4-8 are enlarged viewsof the valve unit 240 with the valve elements thereof shown in variouscontrol positions.

Fig. 4 shows the valve unit 240 with the interconnected two-piece valves241, 245 thereof shown in the downshifted or Second speed positionsbefore initiation of their upshift Direct drive positions. The valveunit 246 has a three-step bore with the larger diameter of the bore atthe left end receiving the valve lands 241:1 and 241C of valve 241 thatare interconnected by the reduced diameter neck portion 241]). The rightend of the valve 241 has a reduced diameter land portion 241x! thatcontains an axially extending bore 241i. Fixedly mounted in the Valvebore 24U, by a press fit or the like, is a cup-like sleeve 256. Theright end portion 256e of the cup-like sleeve 256 is slotted so as toprovide a means whereby the headed stem 245e on the left end of valveelement 245 may be interconnected with sleeve 2556 of valve 24d so as topermit a limited relative axial movement between the spool typeinterconnected valve elements 2M and 245. Valve element 245 comprises apair of spaced apart valve lands Zdband 24M that are interconnected by areduced diameter neck portion 245C. lt will be noted that valve lands2455 and 245e? are of a smaller diameter than either of the lands 241g,241C or 24M of valve 241. This is of importance when considering theopposed pressure fluid generated forces applied to the interconnectedvalves 241 and 245 during automatic and/or driver initiated operation ofthe valves. The valve land Zdd at the right end of valve 245 has anaxially extending bore 245e that receives the compression type valvespring 243. Spring 243 tends to continuously urge the valves 245, 241towards the left end of the stepped valve bore to the positions shown inFig. 4.

With the valves 241, 245 positioned as shown in Fig. 4, governorpressure, that is a pressure fluid responsive to the speed of thetransmission output shaft 31, is directed into the valve bore chamber247 at the left end of valve 240 by means of conduit 98a. At low outputshaft speeds the pressure of the governor pressure in chamber 247 is nothigh enough to shift the valves 241, 245 to the right against theopposing leftwardly directed forces applied to the right end of valve245. Not only does the spring 243 exert a leftwardly directed force onthe valves 243i, 24S, but in addition there is a force applied to theright end of valve 241 due to the throttle pressure fluid existing inthe valve bore chamber 257 at the right end of the stepped valve bore.Throttle pressure fluid, that varies between ten and ninety (lO- 90) p.s. i. is supplied to valve chamber 257 by the conduit 256. When valves241, 245 are in their downshifted positions, shown in Fig. 4, thenconduit 250 can pass throttle pressure fluid through` the valve boreposition 258 and into bypass conduit 242 that is connected with thechamber 257 at the right end of valve 240.

As the output shaft Sl gains speed the governor pressure in chamber 247at the left end of valve unit 2d@ exerts a progressively increasingforce on the valves 26h?, 241 that tends to shift these connected valvestowards the right. Fig. 5 shows the valves 2st. 245 after a substantialamount of rightward shift of the valves 2M, 245 but prior to theposition where snap over et the valves to their upshifted positions(Fig. 6) occurs. it will be noted that in the Fig. 5 position of thevalves 245, Zal, that the valve land 241e has shifted rightward toposition where it has closed oii supply of throttle pressure fiuid fromconduit 25d to the valve bore portion 25S, conduit 242 and to theconnected bore chamber 257 at the right end of the valve unit. It willalso be noted that valve bore portion 25S and the connected bore chamber257 at the right end of the valve `240 have now been connected to adrain or pressure relief outlet through the vent V1. Vent V1 isconnected through the kicldown valve 230 to vent Va (sce Figs. 4 and 6).This venting of chamber 257 has removed the force of the throttlepressure acting on the right end of valve M5 which force has previouslybeen urging the valves Zd, di towards the left in opposition to therightwardly directed force exerted on the valves by the governorpressure in chamber 247. it will also be noted that the line pressuresupply conduit lllta is still closed oli from the bore of the valve 24@by the land 2f/5d of valve 245. Thus line pressure, to accomplish theupshift to `direct drive, is not directed into the valve bore portion 29and into the conduits ldd and i6? until after the valves 2411i, 24S haveupshifted to the right to a greater degree than shown in Fig. 5.

With the venting the throttle pressure from the bore chamber 257 by theuncovering of Vent V1, due to governor pressure in bore chamber 247forcing the valves 24d, 245 rightward toI the positions shown in Fig. 5,the previously existing force equilibrium applied to the valves 21H,2&5' is destroyed.

The removal of the throttle pressure generated force at the right end ofvalve 245 leaves only the spring 2% acting on the valves 241, 245forcing them leltward and thus the "'governor7 pressure generated forceapplied to the left end of valve Zal becomes predominant and snaps thevalves 24F., 245 vtowards the right end of the valve bore (see Fig. 6).

As valves 24T., 24S are snapped towards the right end or the valve bore,the line pressure inlet port from conduit M951 is uncovered and linepressure is admitted to the bore portion 259 (see Fig. 6). Line pressureadmitted to bore portion 259 of valve 24d passes out through conduitlett to the ol or release chamber tc of Second servo 6d. This releasesthe Second brake band 65 and prepares the transmission for theengagement of the Direct clutch C. At the same time that line pressureiluid is passed into conduit lofi it will be noted that line pressnr isalso passed into the branch conduit 2611i. Branch conduit 269diagrammatically represents the connected conduits 163g, letto, 1o9a,269 (see Fig. 3) that connect conduit led to conduit le@ so 'that linepressure will also be directed ,into the apply chamber 55d of Directclutch C at the same time that Second band 65 is released. Thus it willbe seen that Second band 65 is released at the same time that Directclutch C is applied so as to accomplish the upshift from Second toDirect Drive. Also the pressurizing of the conduit i@ with line pressureintroduces line pressure to the bore portion 263. of valve 24th and thiseitects relative movement and elongation of the connected valves 243i,245.

The branch conduit 25d not only provides for the simultaneoustie-activation of Second servo on activation of Direct clutch C, but inaddition, branch conduit 260 provides for the application of linepressure to the bore chamber 261i of valve unit and to the bore 21H;t inthe right end of valve 241. This pressurizing of the valve bore chamber261 applies line pressure to the left end of valve 245 and shifts thevalve 245 to its extreme rightward position (Fig. 6). During this finalportion of the rightward shift of valves 241, 245 there is limitedrelative axial movement or elongation between valves 241i and 245 of anamount equal to the length of 'the neck 245e of valve 245. The land 241eof valve 243i seats against the step liange 262 of the valve unit 2d@after the snap over of valves 215i, to their unshifted posi tion (Fig.6). This relative axial movement between the valves 24.2., Zd' due tothe interconnected valve neck portion 245e and valve sleeve 255 afterthe snap over upshift provides for the successive closing ott of theinlet port of the throttle pressure supply conduit 25d and uncovering ofvent V1 before the line pressure from supply conduit ll9a is admitted tothe valve bore `portion essere 11 259 on a valve upshift. This limitedrelative movement between the valves 241, 245 is also of importance ondownshift of the valves 241, 245 as will be explained subsequently.

It will be noted, when the valves 241, 245 have upshifted to thepositions shown in Fig. 6, that the throttle pressure inlet to the leftend of the valve bore from conduit 25d is closed olf by the land 241e ofvalve 241. Accordingly, the valves 241, 245 in their upshifted positionare not throttle pressure responsive and nor nal Opening and closing ofthe throttle valve will not, in and of itself, cause undesired shiftingor hunting ot the connected shift valves 241, 245. The valves 241, intheir upshifted positions are purely output shaft speed or governorpressure responsive as will hcreina er be explained.

Looking at Fig. 6, it will be noted that in the upshifted position ofthe valves 241, 245, the valve 245 permits line pressure from conduit119e to pass through valve bore portion 259 and through the conduit 2d@to conduit 169 so that the valve chamber 261 of valve unit 24d, as wellas the valve bore 24-1f of valve 241, is pressurized with line pressureliuid. Under such conditions the only force acting on the connectedvalves 241i, 245 that tends to downshift these valves to the left is theforce of compressed springs 243 and that force caused by line pressureacting on the outer peripheral portions of the right end of valve land241d of valve 241. This force is equal to the line pressure multipliedby the difference in area between the end area of valve land 24M ofvalve 241 and the end area of valve land 245]? of valve 245. This linepressure generated valve downshifting force is opposed by the governorpressure generated force caused by the governor pressure in valvechamber 247 acting on the left end of valve land 241e of valve 241.Accordingly, a normal downshift from Direct drive to Second will occurwhen the force of the line pressure acting on the outer peripheralportion of the right end of valve land 241d exceeds the force resultingfrom governor pressure acting on the left end of valve land 241:1. ltwill be noted that there is a great difference in area over which theline and governor pressures act so normally the automatic downshiftwould occur at a relatively low vehicle speed such as between --10 milesper hour although this can be adjusted readily. Due to the nature of thedownshifting forces a very exact point of normal downshift can bedetermined. After the spring 243 and the line pressure initiateddownshift force have moved connected Valves 241, 245 to the leftsufficiently to uncover the throttle pressure inlet from conduit 25@ tovalve bore portion 258, then the throttle pressure is transferred by thebypass conduit 242 to the chamber 257 at the right end of Valve unit241D. Thereafter, a throttle pressure generated force as well as thespring force of spring 245 act on the valves 241, 245 snaps themleftward in opposition to the governor pressure generated force urgingthe valves 241, 245 rightward. Subsequent upshifting to the right ofValves 241, 245 is accomplished by the snap action upshift previouslyexplained. As previously pointed out with regard to the elongation ofvalves 241, 245 on upshift, the elongation is also important ondownshift. Due to the valves 241, 245 being elongated on the beginningof downshift, the inlet port from throttle pressure supply conduit 25dis uncovered before the inlet port from line pressure supply conduit11911 is closed olf by valve land 245e'. Thus a throttle pressure forceis built up in the bore chamber 257 to snap the valves 241, 245 todownshi'fted positions as the line pressure is vented from the borethrough vent V2.

In addition to the normal output shaft speed responsive downshift ofvalves 241, 245, there is also provided a driver or operator controlledkickdown whereby the transmission may be downshifted at anytime, withina 12 A predetermined upper speed safety limit, from Direct drive toSecond speed. Such a kickdown is useful for sudden Yacceleration or formeeting extreme torque load conditions. Figs. 7 and 8 show respectivelytirst the positions of the valves 241, 245 on initiation of a kickdownby a sudden depression of the accelerator pedal G, and second theposition of these valves 241, 245 after beginning of the lricirdown whenthe valves have reached a point where they are about to be snapped overto their downshitted Second speed positions. Due to the particulararrangement and construction of the valves 241, 245 an extremely fast,smooth kiclidown or driver controlled downshilt from Direct drive toSecond speed is readily obtainable.

Considering Fig. 3 as well as Fig. 7, it will be noted that theaccelerator pedal G is connected by linkage .116, 23E. to the kickdownvalve element 232. A substantially full depression of the acceleratorpedal G to at least its last 5 or l0 degrees of throttle openingmovement will cause the linkage 231 to shift the kickdown valve element232 to the right (see Fig. 7) suiiiciently to unseat valve land 232e andpermit line pressure from conduit 119e to pass through valve boreportion 259 and exit into conduit 263. Conduit 268 contains a ilowrestriction 269 and is connected to the bore chamber 233 at the rightend of valve 2.3i?. Line pressure of approximately p. s. i. that isadmitted to the bore of kickdown valve 23d is reduced to a pressure ofabout 50460 p. s. i. by the perforated pressure relief valve 235. Thusthe pressure of the iluid in conduit 268 on the kickdown valve side ofrestriction 269 is less than line pressure and may be called a reducedor compensated line pressure or the kickdown pressure. When the kickdownvalve 232 has been shifted to the right by a substantially fullaccelerator pedal depression, then this 50-60 p. s. i. lziclrdownpressure iluid can pass from the kickdown valve bore 233 through valvebore portion 236 and into conduit 27@ that applies the kickdown pressurefluid to Valve bore portion 253. As bypass conduit 242 connects thevalve bore portion 253 with the bore chamber 257 at the right end ofvalve unit 240, it is thought to be obvious that on a kickdown rof theaccelerator G there will suddenly be applied to the right end of valve245 a substantial leftwardly directed force resulting from thepressurizing of chamber 257 with lrickdowu pressure Huid ofapproximately 5ft-60 p. s. i. With the application of the kickdownpressure to the bore portion 253 and to the bore chamber 257, lettwardlydirected forces are applied to the valves 241, 245 that initiate adownshifting movement of these valves towards the left. in addition tothe force of the kiekdown pressure in the bore portion 257 it will benoted that bore portion 271 is pressurized with kickdown pressure andthis constantly acts on valve land 241e urging the valves 241, 245leftward. Leftward movement of the valves 241, 245 is initiated byresultant of the force of the spring 243 and the force of the lcickdownpressure in bore portions 257, 258, 271. This leftwardly directed forceis suliiciently large to overcome the force of the governor pressure inthe valve chamber 247 at the left end of the valve unit 248i and beginthe downshitting movement of the valves 241, 245. However,- to insure aquick positive downshifting movement of the valving 241,245, the portingin the valve unit 246 is so arranged that after initial leftwardmovement of the valves 241, 245 they approach a snap over downshiftposition such as is shown in Fig. 8.

When the valves 241, 245 have shifted leftwardly to the positions shownin Fig. 8, then the inlet port from conduit 279 to bore portion 258 isclosed oif by land 241tof valve 241 so kickdown pressure from conduit270 is cut off from the chamber 257 at the right end of valve 245.However, at the time the valve land 2411: cuts oft the supply of the50-60 p. s. i. kckdown pressure to the bore portion 258 there issimultaneously applied to bore portion 258 a relatively high throttlepressure of approximately 85-90 p. s. i. due to the `uncovering of theinlet port from conduit 250 by the leftward movement of the valve land241e of valve 241. Accordingly, at the snap over point a significantincrease in leftwardly directed force is applied to the valves Zell, 245that quickly shifts these valves leftwardly to their fully downshiftedpositions corresponding to those shown in Fig. 4. It will be noted thatin the Fig. 8 position `of the valves 241, 245, the valve land 24lc hasisolated the kickdown pressure from the bore portion 25% but the borechamber 271 is still filled with kickdov/n pressure of approximately50-60 p. s. i. while the bore chamber 257 is filled with throttlepressure of approximately 85-90 p. s. i. This combination of highthrottle pressure and kickdown pressure generated forces is more thansufficient to snap the valves 241, 245 over to their normal downshiftedposi tions (see Fig. 4). It is thought to be clear that the kickdownpressure in bore portion 271 will exert a leftwardly directed force onthe valve 241 due to the difierence in diameters of the valve lands 241Cand 241:1. Also the increase in leftwardly directed force applied to theright end of valve land 245 at the snap over point is quite significantfor it is equal to the area of the right end of valve land 245d timesthe difference between the high throttle pressure of SL90 p. s. i. andthe kickdown pressure of 50-60 pf s. i. It is thought to be obvious thatthe kickdown pressure in bore portion 271 of valve unit 240 is reducedto Zero when the downshift is completed for the line pressure supplyfrom conduit 119a is closed off.

While the valve unit is Shown as including a compression type spring 243in the bore chamber 257, it is thought to be obvious that this springcould be omitted and throttle pressure alone be relied on to oppose thegovernor pressure and control the shifting of valves 241 and 245.

Fig. 9 is a fragmentary sectional elevational view of the left end of avalve unit 280 that is similar to the valve unit 240 in that theconnected, two-piece valve elements 281, 285 thereof are sustantiallyidentical to the valve elements 241, 245 of valve unit 240. However,there is one significant difference between the valve units 240 and 280and that is that the valve 281 is so constructed and arranged in thevalve unit 280 that the connected valve elements 281, 285 are responsiveto throttle pressure on both upshift and downshift whereas the valveelements 241, V245 of valve unit 240 are responsive to throttle pressureonly on upshift. Comparing Fig. 6 with Fig. 9 which views each show therespective valve elements 241, 245 and 281, 285 in their fully upshiftedpositions, it will be noted that in Fig. 6 the throttle pressure inletport from conduit 250 is closed oil completely by valve land 241e ofvalve 241 so that the valves 241, 245 are not responsive to throttlepressure as regards normal downshifting. However, in Fig. 9 it will benoted that the valve land 281e of valve 23d does not completely closeoil the throttle pressure inlet port from conduit 259 when valves 281,285 are completely upshifted. Accordingly, opening the throttle valve12d' when the valves 251, 285 are upshifted will always apply adownshifting force to the right end of valve land 281e and thus somevariation in the point lat which downshift from Direct to Second speedwill occur can be achieved depending on the relationship betweengovernor pressure and throttle pressure. The throttle pressureresponsive downshift force can be controlled I'ny varying the relativesizes of the diameters of the valve lands 281a and 28119 of the valve281. In all other respects valve 280 is similar to valve 240 so furtherdiscussion of the valve 280 is considered unnecessary.

It is thought to be clear from the foregoing description that there isherein disclosed an improved, simplified form of valve unit that isparticularly adapted for con trolling speed ratio changes in ahydraulically operated, motor vehicle power transmission system.However, it is obvious that such a valve unit can be used in any -sortof hydraulic control system wherein several dierent pressure fluidsources are utilized to control the operation of a device. The inventionis not to be considered limited by the specific description but merelyby the appended claims.

I claim:

l. In an hydraulically operated control system for an engine drivenmotor vehicle power transmission unit, a pair of pressure fluidoperated, speed ratio drive, control mechanisms arranged for alternateactivation to provide means for selectively transmitting a pair ofdifferent speed ratio drives through said transmission unit, a source ofline pressure fluid, a first conduit means connecting said source ofline pressure fluid to each of said control mechanisms, an automaticallycontrolled, differential pressure operated, valve unit connected to saidrst conduit means and arranged so as to control the supply of linepressure fluid to the said control mechanisms, said valve unitcomprising a valve bore having mounted therein a pair of axiallyaligned, interconnected, relatively axially movable valves arranged forconjoint and independent axial reciprocation in said bore, a source ofpressure fluid having a pressure responsive to the speed of the motorvehicle, a second conduit means connecting said source of vehicle speedresponsive pressure fluid to a rst one of said differential pressureoperated valves, a throttle valve movable between open and closedpositions for controlling the torque transmitted by the motor vehicleengine, a source of pressure fluid controlled by the movement of saidthrottle valve providing a source of pressure fluid having a pressureresponsive to the degree of opening of the throttle valve, a thirdconduit means connecting the source of throttle valve responsivepressure fluid to a second one of the differential pressure operatedvalves in a manner whereby the vehicle speed responsive pressure fluidand the throttle valve responsive pressure fluid exert opposing forcesupon the connected differential pressure operated valves to effectreciprocation thereof, and a resilient means arranged to continuouslyexert a force on the differential pressure operated valves that opposesthe force of the vehicle speed responsive pressure fluid, saiddifferential pressure operated valves being movable by said vehiclespeed responsive pressure fluid to a first limiting position wherein theapplication of the throttle valve responsive fluid to said second one ofsaid valves is prevented vent means arranged to be connected to thevalve unit when said valves have been moved to said first limitingposition to vent the pressure fluid responsive to the degree of openingof the throttle valve and eliminate its effect on movement of saidvalves after which said vehicle speed responsive pressure fluid iseffective to snap said valves to a limiting position wherein the linepressure connected to said valve unit may be applied to said controlmechanisms.

2. In an hydraulically operated control system for an engine drivenmotor vehicle power transmission unit, a pressure fluid operated, speedratio drive, control mechanism, a source of line pressure fluid,I afirst conduit means connecting said source of line pressure fluid tosaid control mechanism, an automatically controlled, differentialpressure operated, valve unit connected to said rst conduit means andarranged so as to control the supply of line pressure fluid to the saidcontrol mechanisrns, said valve unit comprising a valve bore havingmounted therein a pair of axially aligned, interconnected, relativelyaxially movable valves which are arranged for movement axially of thebore, a source of pressure fluid having a pressure responsive to thespeed of the motor vehicle, a second conduit means connecting saidsource of vehicle speed responsive pressure fluid to a rst one of saiddifferential pressure operated valves, a throttle valve movable betweenopen and closed positions for controlling the torque transmitted by themotor vehicle engine, a source of pressure fluid controlled by themovement of said throttle valve providing a source of pressure fluidhaving a pressure responsive to the degree of opening of the throttlevalve, a third conduit means connecting the source of throttle valveresponsive pressure uid to a second one of the differential pressureoperated valves in a manner whereby the vehicle speed responsivepressure uid and the throttle valve responsive pressure tluid exertopposing forces upon the connected differential pressure operated valvesto effect reciprocation thereof, and a resilient means arranged tocontinuously exert a force on the diterential pressure operated valvesthat oppose the force of the vehicle speed responsive pressure uidapplied to said valves, a vent port in the valve bore of saiddifferential pressure operated valves for selectively releasing thethrottle valve responsive pressure tuid that is applied to said secondone of said differential pressure operated valves, said vent port beinglocated such that it is uncovered after the vehicle speed responsivepressure fluid has moved said diterential pressure operated valves to aiirst predetermined position wherein the valves are positioned such thatthe supply of throttle valve responsive pressure tluid to said valvebore is cut ol whereby an unbalanced force acts on said valves to snapsaid valves to a rst limiting position that permits Said line pressureto be applied to said pressure luid operated control mechanism.

3. In an hydraulically operated control system as set forth in claim 2wherein snapping of said valves to said rst limiting position, permitsline pressure to be applied to said valves in such a manner as to etectrelative axial movement between said valves to thereby condition saidvalves for a snap action shift of said valves to their second limitingposition.

4. in combination an engine driven shaft, an accelerator pedal operatedthrottle control for the engine, a hydraulic torque converter drivinglyconnected to said engine driven shaft, a change speed transmission unitof the planetary gear type drivingly connected to said torque converterand comprising input and output shafts having a plurality of planetarygear trains selectively connectible therebetween to provide for thetransmission of a plurality of different speed ratio drives between saidshafts, lluid pressure operated servo mechanisms for controllingactivation and de-activation of said planetary gear trains, and a liuidpressure operated control system for said servo mechanisms comprising anengine driven constant pressure liuid supply source having conduit meansconnecting said supply source to said servo mechanisms, an output shaftspeed responsive governor connected to said fluid pressure supply sourceto provide a source ot governor pressure proportional to the speed ofsaid output shaft, and a driver controlled manually operable speed ratioselector valve connected by conduit means to said uid pressure supplysource and to said servo mechanisms to provide for driver selection of astarting speed ratio drive, an accelerator pedal operated pressureregulating valve unit connected by conduit means to said fluid pressuresupply source adapted to provide a source of throttle pressuresubstantially proportional to the degree of opening of the enginethrottle control, an automatically operable speed ratio control valveunit to eiect automatic upshifts and downshitts between said startingspeed ratio drive and another speed ratio drive with variations in thedifferential pressure relationship existing between said governorpressure and said throttle pressure comprising a valve cylinder with abore therein having a pair of interconnected, relatively axiallymovable, shift control valves slidably mounted therein, conduit means toapply said throttle pressure to one of said' shift valves to urge saidshift valves in one axial direction, conduit means to apply saidgovernor pressure to the other of said shift valves to urge shift valvesin the 16 f opposite axial direction, tuid ow means controlled by themovement of one of said shift valves in one axial direction controllingconnection of said fluid pressure supply source to said servo mechanismsto provide means to automatically effect operation of said servomechanisms, a predetermined movement of the other of said shift valvesin said one axial direction activating vent means arranged fordiscontinuing the application of the throttle pressure to said one ofsaid shift valves to thereby permit snap action shift of said shiftvalves in one axial direction due to the predorninating force of thegovernor pressure applied to said valves.

5. In an hydraulically operated control system, a valve unit comprisinga cylinder with a pair of axially spaced valve receiving bores connectedby a pressure chamber located therebetween, a tirst valve reciprocablymounted in one of said bores, said first valve having portions extendinginto said pressure chamber, resilient means normally positioning saidfirst valve in said one bore and urging said first valve towards saidother bore, a second valve reciprocably mounted in said other borehaving portions engageable with said extending portions of said rstvalve and interconnecting said valves for limited relative axialmovement, a tirst pressure fluid supply connected through certainportions of said other bore to certain portions of said one bore suchthat passage of said first pressure fluid through said certain portionsof said other bore to said one bore is controlled by the location ofsaid second valve in said other bore, a second pressure fluid supplyconnected to other portions of said other bore, a third pressure fluidsupply connected to other portions of said one bore and arranged to beadmitted to said other portions of said one bore after a predeterminedaxial movement of said first valve away from its normal position,conduit means connected between said other portions of said one bore andsaid pressure chamber whereby pressure uid admitted to said otherportions of said one bore from said third pressure uid supply is appliedto said pressure chamber to etect relative axial movement between saidrst and second valves to increase the etective length of said connectedvalves.

6. ln an hydraulically operated control system, a valve unit comprisinga cylinder with a pair of axially spaced valve receiving bores connectedby a pressure chamber located therebetween, a rst valve reciprocablymounted in one of said bores, resilient means normally positioning saidfirst valve in said one bore and urging said first valve towards saidother bore, a second valve reciprocably mounted in said other bore,means extending between said rst valve and said second Valveinterconnecting said valves for limited relative axial movement, a firstpressure tiuid supply connected through certain portions of said otherbore to certain portions of said one bore such that passage of said trstpressure fluid through said certain portions of said other bore to'saidoneV bore is controlled by the location of said second valve in saidother bore, a second pressure uid supply connected to other portions ofsaid other bore that are continuously isolated from said certainportions thereof, a third pressure tuid supply connected to otherportions of said one bore that are continuously isolated from saidcertain portions thereof, said third pressure uid supply inlet to saidone bore being and arranged to admit pressure iluid to said otherportions of said one bore after a predetermined axial movement of saidfirst valve away from aligned, valve receiving bores and. apressure:chamber connected therebetween, a first valve .reciprocably mounted inone of said bores, said first valve having portions thereof extendinginto said pressure chamber, resilient means normally positioning saidfirst valve in said one bore and urging it towards said other bore, asecond valve reciprocably mounted in` said other bore having portionsengageable with said extending portions of said first valve andinterconnecting said valves` for limited, relative Iaxial movement, afirst. pressure fluid supply conduit con nected to said one bore andarranged to have flow therethrough controlled by the` location of saidsecond valve in said other bore,` a second pressure fluid supply conduitconnected to said other bore, saidrst and second pressure fluid supplyconduits providing means for applying opposing, axially directed,pressure fiuid generated, forces to said first and second valves, athird pressure fluid supply conduit connected to said one bore at a`location such that the pressure fiuid entering said one bore therefromdoes not effect axial movement of said valves, the bore inlet from saidthird conduit being arranged to be uncovered by axial movement of saidfirst valve to a first limiting position, conduit means connectedbetween said third pressure fluid supply bore inlet and said pressurechamber when said first valve is in said first limiting position wherebypressure fiuid admitted to said one bore from said third pressure fiuidsupply conduit is applied to said pressure chamber to effect relativemovement between said first and second valves to increase the effectivelength of said connected valves.

8. In an hydraulically operated control system, a valve unit comprisinga cylinder with a pair of spaced, axially aligned, valve receiving boresand a pressure chamber connected therebetween, a first valvereciprocably mounted in one of said bores, said first valve having`portions thereof extending into said pressure chamber, resilient meansnormally positioning said first valve in said one bore and urging ittowards said other bore,` a second valve reciprocably mounted in saidother bore having portions engageable with said extending portions ofsaid first valve and interconnecting said valves for limited, relativeaxial movement, a first pressure fiuid supply conduit connected to saidone bore and arranged to have liow therethrough controlled by thelocation of said second valve in said other bore, a second pressurefiuid supply conduit connected to said other bore, said first and secondpressure liuid supply conduits providing means for applying opposing,axially directed, pressure fluid generated, forces to said first andsecond valves, a third pressure fiuid supply conduit `connected to saidone bore at a location such that the pressure fluid entering said onebore therefrom does not effect axial movement of said valves, the boreinlet from said third conduit being arranged to be uncovered by axialmovement of said first valve to a first limiting position, conduit meansconnected between said third pressure uidsupply bore inlet and saidpressure chamber when said first valve is in said first limitingposition whereby pressure fluid admitted to said one bore from saidthird pressure fluid supply conduit is applied to said pressure chamberto effect relative movement between said first and second valves toincrease the effective length of said connected valves, a first ventport arranged to be connectedv to said one bore prior to axial shift ofsaid first` valve to saidfirst limiting position and a second vent port`arranged to be connected to said second bore prior to shift of saidfirst valve to said first limiting position.

9. In an hydraulically operated control system, a first valve unitcomprising a cylinder with a pair of spaced, axially aligned, valvereceiving bores and a pressure chamber connected therebetween, al firstvalve reciprocably mounted in` one of said bores, said first valvehaving portions thereof extending into. said pressure chamber, resilientmeans normally positioning said first valve in said one bore and urgingit` towards said other bore, a

flow therethrough controlled by the location of said sec,-A

ond valve in saidiother bore, a second pressure fluid supply conduitconnected to said other bore, said` first and second pressure fluidsupply conduits providing means for applying opposing, axially directed,pressure fiuid generated, forces to said first and second valvestoeffectautomatic operation thereof, a third pressure fluid supply conduitconnected to said one bore at a location such that the pressure fluidentering said one bore therefrom does not effect conjoint axial movementof said valves, the bore inlet from said third conduit being arranged tobe uncovered by axial movement of said first valve` to a first limitingposition, conduit means` connected between said third` pressure liu-idsupply bore inlet and said pressure chamber when said first valve is insaid first limiting position whereby pressure huid admitted to said onebore from said third pressure fluid supply conduit is applied to saidpressure chamber to effect relative movement between said first. andsecond valves to increase the effective length of said connectedvalves,` a first vent port arranged to be connected to said one bore ofsaid firs-t valve prior to axial shift of said first valve to said firstlimiting position and a second vent port arranged to 'be connected tosaid other bore of said first valve prior to shift of said first valveto said first limiting position and a second valve unit comprising aycylinder bore mounting an, axially reciprocable, operator operablevalve adapted to provide means to overrule the automatic operation ofthe valves of said first valve unit, `said second' valve unit cylinderbore having a first bore portion connected by conduit means to thoseportions of said one bore of said first` valve unit that are suppliedwith pressure fiuid from said third pressure fluid supply conduit whensaid first valve of said first valve unit is in said first limitingposition and a second bore portion in said second valve unit cylinderbore connectible to the first bore portion thereof by operation of saidsecond valve unit operable valve, said second bore portion being`connected to those portions of the other bore of said first valve unitthat are arranged to be connected to said one bore of the first valveunit.

l0. In an hydraulic control system as set forth in claim 9 wherein thesecond bore portion of said second valve unit has a pressure reliefvalve to control the pressure applied to the valves of said first valveunit by operation of said second valve unit.

ll. In an hydraulic control system as set forth in claim 9 wherein theconduit means connecting the said one bore of the first valve unit tothe said first bore portion of said second valve unit includes pressurefiuid flow restriction means.

l2. ln an hydraulically operated control. system a valve unit comprisinga cylinder having a pair of axially spaced valve bores with an axiallyaligned pressure chamber connected therebetween, a rst valvereciprocably mounted in one of said bores, said first valve havingportions` thereof extending into said pressure chamber, resilient meansnormally urging said first valve towards said other bore, a second valvereciprocably mounted in said other bore having portions thereofinterconnected with the extending portions of said first valve so as topermit limited, relative axial movement between said valves, conduitmeans arranged to connect certain portions of said one bore to saidpressure chamber when said first valve is moved in one axial directionto a predetermined position in said one bore, a first pressure fluidsource connected to other portions of said one bore providing means tourge said connected valves ini the opposite axial direction, a secondpressure fluid source` connected to4 said other bore providing means tokurge said connected valves in said one axial direction, a third pressurefluid source connected to said certain portions of said one bore, afirst vent port connected to said certain portions of said one borearranged to vent said pressure chamber when said first valve ispositioned in said one bore so as to close off said third pressure fiuidsource from said certain portions of said one bore, and a second ventport connected to portions of said other valve bore that arecontinuously separated from the portions thereof acted on by said secondpressure fluid source.

13. In a hydraulically operated control system, a valve unit comprisinga cylinder having a pair of axially spaced valve bores with an axiallyaligned pressure chamber connected therebetween, a first valvereciprocably mounted in one of said bores, said rst valve havingportions thereof extending into said pressure chamber, resilient meansnormally positioning said first valve in said one bore and urging saidfirst valve towards said other bore, a second valve reciprocably mountedin said other bore having portions thereof interconnected with theextending portions of said first valve so as to permit limited, relativeaxial movement between said valves, conduit means arranged to connectcertain portions of said one bore to said pressure chamber when saidfirst valve is moved in one axial direction from its normal position toa predetermined position in said one bore, a first pressure fiuid sourceconnected through certain portions of said other bore to other portionsof said one bore providing means to urge said connected valves in theother axial direction, a second pressure fluid source connected to otherportions of said other bore providing means to urge said connectedvalves in sai-d one axial direction, a third pressure fluid sourceconnected to said certain portions of said one bore, a first vent portconnected to said certain portions of said one bore arranged to ventsaid pressure chamber when said first valve is positioned in said onebore so as to close off said third pressure fiuid source from saidcertain portions of said one bore, and a second vent port connected tosaid certain portions of said other valve bore and arranged such that itis closed off from said certain portions of the other valve bore by saidsecond valve when the first source of pressure fluid is connectedthrough said certain portions of said other bore.

14. In an hydraulically operated control system, a valve unit comprisinga cylinder with a pair of axially spaced valve receiving bores connectedby a pressure chamber located therebetween, a first valve reciprocablymounted in one of said bores, resilient means normally positioning saidfirst valve in said one bore and urging said first valve towards saidother bore to a first limiting position, a second valve reciprocablymounted in said other bore, means extending between said valvesinterconnecting said valves for limited relative axial movement, a firstpressure fluid supply connected through certain portions of said otherbore to certain portions of said one bore such that passage of pressurefiuid from said first pressure fiuid supply through said certainportions of said other bore to said certain portions of said one bore iscontrolled by the location of said second valve in said other bore, asecond pressure fiuid supply connected to other portions of said otherbore which other portions are continuously isolated from said certainportions of said other bore, the application of pressure fluid from saidfirst and second pressure fluid supplies to said valves being in opposedrelationship such that the pressure differential therebetween effectsconjoint axial movement of said valves, a third pressure fluid supplyconnected to other portions of said one bore that are continuouslyisolated from said certain portions of said one bore, the supply ofpressure fluid from said third source to said other portions of said onebore occurring after a predetermined axial movement of said first valveaway from its normal first limiting position, conduit means connectedbetween said other portions of said one bore and said pressure chamberwhereby pressure fluid from said third supply admitted to said otherportions of said one bore is applied to said pressure chamber to effectrelative axial movement between said first and second valves to increasethe effective length of said connected valves.

15. In an hydraulically operated control system, a valve unit comprisinga cylinder with a pair of axially spaced valve receiving bores connectedby a pressure chamber located therebetween, a first valve reciprocablymounted in one of said bores, resilient means normally positioning saidfirst valve in said one bore and urging said first valve towards saidother bore to a first limiting position, a second valve reciprocablymounted in said other bore, means extending between said valvesinterconnecting said valves for limited relative axial movement, a firstpressure fiuid supply connected through certain portions of said otherbore to certain portions of said one bore such that passage of pressurefluid from said first pressure fluid supply through said certainportions of said other bore to said certain portions of said one bore iscontrolled by the location of said second valve in said other bore, asecond pressure fluid supply connected to other portions of said otherbore which other portions are continuously isolated from said certainportions of said other bore, the application of pressure fluid from saidfirst and second pressure fiuid supplies to said valves being in opposedrelationship such that the pressure differential therebetween effectsconjoint axial movement of said valves, a third pressure fiuid supplyconnected to other portions of said one bore that are continuouslyisolated from said certain portions of said one bore, the supply ofpressure fluid from said third source to said other portions of said onebore occurring after a predetermined axial movement of said first valveaway from its normal first limiting position, conduit means connectedbetween said other portions of said one bore and said pressure chamberwhereby pressure fluid from said third supply admitted to said otherportions of said one bore is applied to said pressure chamber to effectrelative axial movement between said first and second valves to increasethe effective length of said connected valves, a first vent portconnected to said other portions of said one bore, and a second ventport connected to said certain portions of said other bore.

16. In an hydraulically operated control system, a valve unit comprisinga cylinder with a pair of axially spaced valve receiving bores connectedby a pressure chamber located therebetween, a first valve reciprocablymounted in one of said bores, a second valve reciprocably mounted insaid other bore, means extending between said first and second valvesinterconnecting said valves for limited relative axial movement, a rstpressure fluid supply connected through certain portions of said otherbore to certain portions of said one bore such that passage of saidfirst pressure fiuid through said certain portions of said other bore tosaid one bore is controlled by the location of said second valve in saidother bore, a second pressure fiuid supply connected to other portionsof said other bore that are continuously isolated from said certainportions of said other bore, the pressure fiuid applied to said valvesby said first and second pressure fluid supply sources acting on saidvalves in opposed relationship such that the pressure differentialtherebetween effects conjoint axial movement of said valves, a thirdpressure fluid supply connected to other portions of said one bore thatare continuously isolated from said certain portions of said one bore,the pressure fluid from said third supply being admitted to said otherportions of said one bore after a predetermined axial movement of saidfirst valve conduit means connected between said other portions of saidone bore and said pressure chamber whereby pressure fiuid admitted tosaid other portions of said one bore from said third pressure fluidsupply is applied to said pressure chamber to effect relative axialmovement between said first and second valves to increase the effectiveto. be connected toA said other portions of` said one bore whilepressure fluid, supply from said third. source is closed off from saidone bore, and a second vent port connected to said certain portions ofsaid other bore,V said secondf valve being' formed so as to providemeans connecting said second vent port to said certain` portions of saidone bore when said second valve is positioned so as to close o supply ofpressure fluid from said first pres-- sure fluid supply to said certainportions of said one bore.

17. In a hydraulic control system as set forth in claim 16 wherein saidsecond valve is formed such that the pressure fluid from :said secondpressure fluid supply will apply an unbalanced axially -directed forceto said valves after said second valve has moved to a position closingoff the supply of pressure fluid from said first pressure fluid supplyto said certain portions of said one bore.

18'. In an hydraulically operated control system, a first valve unitcomprising a cylinder with a pair of axially spaced valve receivingbores connected by a pressure chamber located therebetween, a firstvalve reciprocably mounted in one of said bores, a second valvereciprocably mounted'in said other bore, means connected between: saidfirst and second valves interconnecting said valves for limited relativeaxial movement, a firstpressure fluid supply source connected throughcertain portions. of said other bore to certain portions of said onebore such that passage of said first pressure fluid through said certainportions of said other bore to said certain portions of said one bore iscontrolled by the location ofV said second valve in said other bore, asecond pressure fluid supply source connected to other portions of saidother bore that are continuously isolated from said certain portions ofsaid other bore, said pressure fluids from said' first and second supplysources applying forces toV said connected valves in opposedrelationship such that axial movement of said valves results from thepressure differential between said first and second pressure fluids, athird pressure tions of said one bore that are continuously isolatedfrom fluid supply source arranged to be connected to other porsaidcertain portions of said one bore, pressure fluid from the third sourcebeing arranged to be admitted to said other portions of said one boreafter a predetermined axial movement of said first valve by the pressurefluid from said second .supply source, conduit means connected betweensaid other portions of said one bore and said pressure chamber wherebypressure fluid admitted to said other portions of said one bore fromsaid third pressure liuid supply is applied to said pressure chamber toeffect relative axial movement between said first and second valves toincrease the effective length of said connected valves, a first ventport arranged to be connected to said other portions of saidone borewhen theY first pressure fluid supply source is connected to saidcertain portions of said one bore, and a second vent port arranged to beconnected to said certain portions of said' other bore when said secondvalve closes off connection of said first pressure fluid `supply sourceto said certain portions of said other bore.

19. In an hydraulically operated control system, a first valve unitcomprising a cylinder with a pair ofr axially spaced valve receivingbores connected by a pressure chamber located therebetween, a firstvalve reciprocably mounted in one of said bores, a second valvereciprocably mounted in said other bore, means connected between saidfirst and second valves interconnecting said valves for limited relativeaxial movement, a first pressure fluid supply source connected throughcertain portions of said other bore to certain portions of said one boresuch that passage of said first pressure fluid through said certainportions of said other bore to said certain portions of said one bore iscontrolled by the location of said second valve in said other bore, asecond pressure fluid supply source connected to` other portions of,said other bore that are continuously isolated from said certainyportions of said other bore, said pressure fluids. from said. first andsecond supply sources applying forces to said connected valves inopposed relationship such that axial movement of said valves resultsfrom` the pressure differential between said first and second pressurefluids, a third pressure fluid supplysource arranged to be connected toother portions of said one bore that are continuously isolated from saidcertain portions of said one bore, pressure uid from the third sourcebeing arranged to be admitted to said other portions of said one boreafter a predetermined axial movement of said first valve by the pressurefluid from said second supply source, conduit means connected be tweensaid other portions of said one bore and said pressure chamber wherebypressure fluid admitted to said other portions of said one bore fromsaid third pressure fluid supply is applied to said pressure chamber toeffect relative axial movement between said first and second valves toincrease the effective length of said connected valves, a first ventport arranged to be connected to said other portions of said one borewhen the first pressure fluid supply source is connected to said certainportions of said one bore, a second vent port arranged to be connectedto` said certain portions of said other bore when said second valvecloses ofi connection of said first pres sure fluid supply source tosaid certain portions of said other bore, and a second operator operatedvalve unit connected between saidother portions of said one bore andsaid certain portions of said other bore of said first valve unit so asto provide means to apply a pressure fluid generated force to saidsecond valve of said first valve unit while. said first pressure fluidsupply source is closed off from said certain portions of said one borewhich pressure fluid generated force will oppose the force of thepressure fluid from said second pressure fluid supply source that isapplied to said second valve of said first valve unit.

20, In an hydraulically operated control system, a first valve unitcomprising a cylinder with a pair of axially spaced valve receivingbores connected by a pressure chamber located therebetween, a firstvalve reciprocably mounted in one of said bores, resilient meansnormally positioning said rst valve in said one bore and urging saidfirst valve towards said other bore to a first limiting position, asecond valve reciprocably mounted in said other bore, means extendingbetween said valves interconnecting said valves for limited relativeaxial movement, a first pressure fluid supply source connected throughcertain portions of said other bore to certain portions of said one boresuch that passage of pressure fluid from said first pressure fluidsupply source through said certain portions of said other bore to saidcertain portions of said one bore is controlled by the location of saidsecond valve in said other bore, a second pressure fluid supply sourceconnected to other portions of said other bore which other portions arecontinuously isolated from said certain portions of said other bore, theapplication of pressure fluid from said first and second pressure fluidsupply sources to said valves being in opposed relationship such thatthe pressure differential therebetween effects conjointaxial movement ofsaid valves, a third pressure fluid supply source connected to otherportions of said one bore that are continuously isolated from saidcertain portions of said one bore, the supply of pressure fluid fromsaid third pressure fluid source to said other portions of said one boreoccurring after a predetermined axial movement of said first valve awayfrom its normal first limiting position, conduit means connected betweensaid other portions of said one bore and said pressure chamber wherebypressure fluid from said third supply admitted to said other portions ofsaid one bore is applied to said pressure chamber' to effect relativeaxial movement between said first and second valves to increase theeffective length of said connected valves, a first vent port arranged tobe connected to said other portions of said one bore, and a second ventport arranged to be connected to said certain portions of said otherbore, and a second operator operated valve unit connected between saidother portions of said one bore and said certain portions of said otherbore of said first valve unit so as to provide means to apply a pressurefluid generated force to said second valve of said first valve unitwhile said first pressure fluid supply source is closed off from saidcertain portions of said one bore which pressure fluid generated forcewill oppose the force of the pressure fluid from said second pressurefluid supply source that is applied to said second valve of said firstvalve unit.

21. In an hydraulically operated control system for an engine drivenpower transmission unit having driving and driven shafts, a pair ofpressure fluid operated, speed ratio drive, control mechanisms arrangedfor alternate activation to provide means for selectively transmitting apair of different speed ratio drives through said transmission unit, asource of line pressure uid, a first conduit means having portionsconnecting said source of line pressure fluid to each of said controlmechanisms, an automatically controlled, differential pressure operated,valve unit connected to said first conduit means and arranged so as tocontrol the supply of line pressure fiuid to the said controlmechanisms, said valve unit comprising a valve bore having mountedtherein a pair of interconnected, relatively movable valves arranged forconjoint and independent movement in said bore, a source of pressurefluid having a pressure responsive to the speed of one of saidtransmission shafts, a second conduit means connecting said source ofshaft speed responsive pressure fiuid to a first one of saiddifferential pressure operated valves, a throttle valve for said enginemovable between open and closed positions for controlling the torquetransmitted by the engine, a source of pressure fiuid controlled by themovement of said throttle valve providing a source of pressure liuidhaving a pressure responsive to the degree of opening of the throttlevalve, a third conduit means connecting the source -of throttle valveresponsive pressure uid to a second one of the differential pressureoperated valves in a manner whereby the shaft speed responsive pressurefluid and the throttle valve responsive pressure liuid exert opposingforces upon the connected differential pressure operated valve to effectmovement thereof, and Vent means to neutralize the effect of thethrottle valve responsive pressure fluid on said valves, saiddifferential pressure operated valves being movable by said shaft speedresponsive pressure fiuid to a first predetermined position wherein theapplication of the throttle valve responsive fluid to said second one ofsaid valve is prevented after which said shaft speed responsive pressureliuid is effective to snap said valves to a ylimiting position whereinthe line pressure connected to said valve unit may be applied to atleast one of said control mechanisms.

22. In an hydraulically operated control system as set forth in claim 21wherein the valves are arranged such that upon movement thereof towardssaid first |limiting position line pressure is applied to said valves toeffect snap action shift thereof.

23. In an hydraulically operated control system as set Y 24 forth inclaim 22 wherein means are provided whereby the line pressure applied tosaid valves as said valves are shifted to said first limiting positionacts on the valves and effects relatively movement between said valves.

24. In an hydraulically operated control system as set forth in claim2l, an operator operable Valve unit connected to portions of saidautomatically controlled valve unit so as to provide a control valve forapplying a pressure fluid to those portions of said automaticallyoperable valves normally acted on by the throttle valve responsivepressure fiuid when the source of throttle valve responsive pressurefluid is disconnected from the valve bore of the automaticallycontrolled valve unit.

25. In an hydraulically operated control system for a control mechanism,a first source of pressure uid, a first conduit means having portionsconnecting said first source of pressure fluid to the control mechanism,an automatically controlled, differential pressure operated, valve-unitconnected to said first conduit means and arranged so as to control thesupply of said first pressure fluid to the said control mechanism, saidvalve unit comprising a valve bore having mounted therein a pair ofrelatively movable valves arranged for conjoint and independent movementin said bore, a source of a second pressure fiuid having a Variablepressure, a second conduit means connecting said second source ofpressure fluid to a first one of said differential pressure operatedvalves, a third source of pressure fiuid providing a second source ofvariable pressure fiuid, a third conduit means connecting the thirdsource of pressure fluid to a second one of the differential pressureoperated Valves in a manner whereby the two variable pressure liuidsexert opposing forces upon the connected differential pressure operatedvalves to effect movement thereof, and vent means to neutralize theeffect of one of the variable pressure fiuids on said valves when thevalves are shifted to a predetermined position, said differentialpressure operated valves being movable by the other `one of saidvariable pressure fluids to said predetermined position after which saidfirst Variable pressure liuid is effective to snap said valves to alimiting position wherein the first source of pressure liuid isconnected to said control mechanisms.

26. In an hydraulically operated control system as set forth in claim 25including an operator `operable valve connected to a source of fiuidpressure and connectible to portions of the valve bore for saidautomatically controlled valve unit, said operator `operable valveproviding means to `apply pressure fluid to the portions of theautomatically operable valve unit normally vented by said vent meanswhen said automatically operable valves are in said limiting positionwhereby a force may be applied to said automatically operable valves toovercome the force applied thereto by said first variable pressurefluid.

References Cited in the file of this patent UNITED STATES PATENTS2,541,391 Weiss et al. Feb. 13, 1951 2,603,943 Everden July 22, 19522,627,189 McFarland Feb. 3, 1953 2,630,895 McFarland Mar. 10,19532,640,373 Iandasek June 2, 1953 2,663,393 Livermore Dec. 22, 1953

